<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <script src="../vue.js"></script>
  </head>

  <body>
    <!-- 
      在vue渲染的过程中 diff算法是一直在工作的,但是diff算法的比较是默认按照顺序依次比较的
      如果说我们逆序添加数据,则很可能diff算法的对比错位了
      所以我们在列表渲染的时候要添加一个唯一的key,diff算法的比较就变成了key对应的新旧虚拟DOM的比较
     -->
    <div id="app">
      <button @click="addPersonBefore">在前边添加一个人</button>
      <button @click="addPersonAfter">在后边添加一个人</button>
      <ul>
        <li v-for="item in persons" :key="item.id">
          姓名：{{item.name}} --- 年龄 {{item.age}}
        </li>
      </ul>
    </div>
    <script>
      Vue.config.productionTip = false;

      const vm = new Vue({
        el: "#app",
        data() {
          return {
            persons: [
              { id: "001", name: "laowang", age: 19 },
              { id: "002", name: "xiaowang", age: 29 },
              { id: "003", name: "zhongwang", age: 9 },
            ],
          };
        },
        methods: {
          addPersonBefore() {
            this.persons = [
              { id: Date.now(), name: "dawang", age: 22 },
              ...this.persons,
            ];
          },
          addPersonAfter() {
            this.persons = [
              ...this.persons,
              { id: Date.now(), name: "wangzhongwang", age: 32 },
            ];
          },
        },
      });
    </script>
  </body>
</html>
